1. Field of the Invention
The present invention relates to a field of optical imaging and spectral sensing. In particular, the present invention relates to non-disruptive continuous and radiometrically accurate calibration of a focal plane array sensor using a global scene motion.
2. Background Art
Advances in a solid state detector technology lead to an increasing use of focal plane array (FPA) detectors for infrared (IR) and visible-light imaging and spectral sensing. Use of FPAs allows compactness, cost-effective production and high performance of sensors, in turn, leading to high sensitivity and resolution. The IR-sensor arrays are applicable to broadband thermal imaging, where maximizing broadband spatial resolution and intensity signal-to-noise ratio is of paramount importance. Some of the examples of use of such FPAs include night-vision systems, airborne and space-based reconnaissance and surveillance systems, astronomical imaging, and forest fire early detection systems.
Other examples of use of such array sensors include spectral sensing. In spectral sensing, different array elements are designed to respond to different wavelengths of light. This allows the sensor to detect the spectrum of the source. Some of the modern day spectral sensors are capable of measuring irradiance at upwards of 200 narrow bands in every point in the image. Some examples of spectral sensors include detection and identification systems for hazardous biological and chemical agents, as well as monitoring systems of environmental changes in lakes and other natural habitats.
However, current technology relating to array-sensors have several drawbacks and disadvantages. One major disadvantage to using modern day array-sensors for quantitative remote sensing is the array's non-uniformity noise. Non-uniformity noise primarily results from minute detector-to-detector dissimilarities due to FPA's pixel-to-pixel variation in the response as well as fabrication related geometrical dissimilarities in individual FPA elements. It is well known, that most modern FPAs suffer from spatial non-uniformity noise. Spatial non-uniformity noise manifests itself in a form of a quasi-fixed pattern, also referred to as fixed-pattern noise (“FPN”). Non-uniformity noise can lead to an inaccurate radiometric measurement, reduced temperature resolvability, and reduced spatial resolution. Furthermore, it has a detrimental effect on the performance of many post-processing enhancement and restoration algorithms that assume temporal noise but not FPN, whose temporal statistics exhibit a high degree of correlation.
Some modern-day array-sensors developed systems for compensation of the non-uniformity noise through an one-time factory calibration of the sensor. However, such systems do not compensate for sensor drift problems over time, thus, making the one time factory calibration ineffective. To correct for sensor drift over time, a constant calibration of the sensor is necessary to correct for non-uniformity in the detector response. However, present day calibration techniques disrupt operation of the array sensor during the calibration process. Furthermore, there are other problems associated with modern day FPA sensors.
Therefore, there is a need for a better focal plane array sensor capable of being continuously calibrated while still detecting images from the scene. Furthermore, there is a need for a focal plane array sensor capable of continuously correcting for non-uniformity drift.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiment described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.